MIPS: Alchemy: introduce helpers to access SYS register block.

This patch changes all absolute SYS_XY registers to offsets from the
SYS block base, prefixes them with AU1000 to avoid silent failures due
to changed addresses, and introduces helper functions to read/write
them.

No functional changes, comparing assembly of a few select functions shows
no differences.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/7464/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/alchemy/board-mtx1.c b/arch/mips/alchemy/board-mtx1.c
index 25a59a2..1e3b102 100644
--- a/arch/mips/alchemy/board-mtx1.c
+++ b/arch/mips/alchemy/board-mtx1.c
@@ -85,10 +85,10 @@
 #endif /* IS_ENABLED(CONFIG_USB_OHCI_HCD) */
 
 	/* Initialize sys_pinfunc */
-	au_writel(SYS_PF_NI2, SYS_PINFUNC);
+	alchemy_wrsys(SYS_PF_NI2, AU1000_SYS_PINFUNC);
 
 	/* Initialize GPIO */
-	au_writel(~0, KSEG1ADDR(AU1000_SYS_PHYS_ADDR) + SYS_TRIOUTCLR);
+	alchemy_wrsys(~0, AU1000_SYS_TRIOUTCLR);
 	alchemy_gpio_direction_output(0, 0);	/* Disable M66EN (PCI 66MHz) */
 	alchemy_gpio_direction_output(3, 1);	/* Disable PCI CLKRUN# */
 	alchemy_gpio_direction_output(1, 1);	/* Enable EXT_IO3 */